The present invention relates to a novel positive-working photoresist composition or, more particularly, to a positive-working photoresist composition of the chemical amplification type having high transparency to the ultraviolet light of the ArF excimer laser beam to exhibit high photosensitivity in pattern-wise exposure to light as well as high pattern resolution and suitable for puddle development with high affinity to an aqueous alkaline developer solution and capable of giving a patterned resist layer having an excellent cross sectional profile of the patterned resist layer which has good adhesion to the substrate surface and exhibits high resistance against dry etchings.
As is known, positive-working photoresist compositions of the chemical amplification type form a class of the most promising photoresist compositions used in the modern photolithographic patterning technology in the manufacture of various kinds of fine electronic devices. The resinous ingredient most widely used in the prior art photoresist compositions of the chemical amplification type is, by virtue of the high transparency to the KrF excimer laser beams of 248 nm wavelength, a polyhydroxystyrene resin of which, optionally, a part of the hydroxyl groups are protected by substituting solubility-reducing groups capable of being dissociated in the presence of an acid.
As a trend in the current photolithographic patterning technology toward finer and finer patterning in the manufacture of semiconductor devices, the conventional KrF excimer laser beam of 248 nm wavelength as the light source for the pattern-wise exposure of the photoresist layer is now under continued replacement with the ArF excimer laser beam having a shorter wavelength of 193 nm.
The above mentioned polyhydroxystyrene-based resinous ingredient, however, is no longer quite satisfactory in the photolithographic patterning process using an ArF excimer laser as the patterning light source because the aromatic structure of the resin is not highly transparent to the light having a wavelength as short as 193 nm. In place of such an aromatic resin of low transparency to the short wavelength light, acrylic resin-based resinous ingredients free from aromatic structures are now highlighted in the photolithographic technology despite the defects thereof that acrylic resins in general are not highly resistant against dry etching which is a step usually involved in the manufacture of semiconductor devices.
As an improvement of acrylic resins in respect of the transparency and dry etching resistance, a proposal is made in Japanese Patent Kokai 4-39665 for a polymer of an acrylate ester having a skeletal structure of adamantane in the ester-forming part of the molecule. Japanese Patent Kokai 5-265212 proposes a copolymer of tetrahydropyranyl acrylate and an acrylate ester having a skeletal structure of adamantane in the ester-forming part of the molecule. A problem in these prior art resins is that the monomers used in the preparation of the resins are very expensive due to introduction of the very specific adamantane structure into the acrylate ester molecules even if it be set aside that a high photosensitivity as desired cannot be obtained with the photoresist composition and the cross sectional profile of the patterned resist layer formed therefrom is not quite satisfactory. Accordingly, the resinous material having an adamantane structure is not suitable for industrial applications to photoresist compositions.
While the photolithographic process using the ArF laser beams has been developed with an important object to obtain a patterned resist layer having fineness of 0.2 .mu.m or even finer with good resolution, a problem to be solved in the use of a conventional acrylic resin as an ingredient in the photoresist composition is that the adhesion between the substrate surface and the resist layer is not high enough sometimes to cause a trouble due to falling of the patterned resist layer.
In view of the above mentioned problems, proposals are made for an acrylic resin of which a part of the monomeric units are derived from an acrylate ester having an oxygen-containing heterocyclic group such as 3-oxocyclohexyl ester group taught in Japanese Patent Kokai 5-346668 and .gamma.-butyrolactone group taught in Japanese Patent Kokai 7-181677.
Though not without improvements in respect of the adhesion to the substrate surface, the above mentioned specific acrylate ester compounds are not suitable for mass production due to the complicated and lengthy synthetic procedure thereof. In addition, due to the relatively low affinity of the resin to an aqueous alkaline developer solution, the puddle development as a major current in the modern photolithographic process cannot be undertaken for the development treatment of the photoresist layer. Accordingly, it is eagerly desired in the photolithographic fine patterning technology to develop a novel and improved photoresist composition suitable for patterning light exposure with ArF excimer laser beams and exhibiting high adhesion of the resist layer to the substrate surface along with good affinity to an aqueous alkaline developer solution to give applicability of the puddle development treatment.
Besides, Japanese Patent Kokai 9-90637 discloses an acrylic resin having monomeric units derived from an acrylate ester which is formed from acrylic acid and a lactone bonded at the .beta.-position, as in mevalonic lactone, with introduction of an alkyl group to the .beta.-carbon atom. The lactone residue, having an alkyl group bonded to the .beta.-carbon atom, is dissociable by interacting with the acid generated from an acid generating agent. The photoresist composition disclosed there is not satisfactory in respect of the photosensitivity and pattern resolution with poor contrast between the pattern-wise exposed areas and the unexposed areas.